The self-association of normal alcohols (1-butanol, 1-hexanol, and 1-octanol) and unsaturated alcohol (cis-9-octadecen-1-ol) in the pure liquid state in decane and in tetrachloride solutions has been studied by near-infrared (NIR) and NMR spectroscopic observations.The mean degree of association obtained for the normal alcohols is approximately four regardless of the hydrocarobon-chain length and inds of the solvent.The higher association number for the normal alcohols compared with that for fatty acids having the same nuber of carbon atoms as the alcohol most likely accounts for their higher viscosity and lower self-diffusion coefficient than those for the fatty acids. The association number for cis-9-octadecen-1-ol (oleyl alcohol) is less than that for normal alcohol. This is because of the steric hindrance of cis-type double bond included in its molecular structure.Almost perfect NIR band assignment in the spectrum were carried out for the series of alkanes ; the absorption band at 1450 nm for alkanes was concluded to be assigned not to CH_2 but CH groups. Relaxation-time study for NMR obviusly showed that the alcohol aggregates dissociate into monomeric molecules with an increase in temperature.